U.S. patent application number 15/994849 was filed with the patent office on 2019-12-05 for increasing the filament count of carbon fiber tows.
The applicant listed for this patent is Hexcel Corporation. Invention is credited to Harini Dasarathy, Adam Dust, Rebecca Forsgren, Robert Loesch.
Application Number | 20190368080 15/994849 |
Document ID | / |
Family ID | 66655476 |
Filed Date | 2019-12-05 |
United States Patent
Application |
20190368080 |
Kind Code |
A1 |
Dust; Adam ; et al. |
December 5, 2019 |
INCREASING THE FILAMENT COUNT OF CARBON FIBER TOWS
Abstract
The filament count of a carbon fiber tow is increased by
spreading and commingling the carbon filaments of a first tow with
the carbon filaments of a second tow. The carbon filaments of the
first and second tows are spread apart using a gas stream. The
spread tows are aligned with each other and brought into contact as
they pass over a grating in the presence of the same or a different
gas stream to form an entangled tow. The entangled tow is then
formed into a combined tow. The modulus and denier of the carbon
filaments in the first and second tows may be the same or they can
be varied to provide combined tows with a wide range of filament
counts and filament combinations.
Inventors: |
Dust; Adam; (Salt Lake City,
UT) ; Loesch; Robert; (Midvale, UT) ;
Dasarathy; Harini; (Huntsville, AL) ; Forsgren;
Rebecca; (West Valley City, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hexcel Corporation |
Dublin |
CA |
US |
|
|
Family ID: |
66655476 |
Appl. No.: |
15/994849 |
Filed: |
May 31, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 70/50 20130101;
D01F 9/00 20130101; D02J 1/08 20130101; D02J 1/18 20130101; D01F
8/18 20130101; D10B 2101/12 20130101 |
International
Class: |
D02J 1/08 20060101
D02J001/08; D02J 1/18 20060101 D02J001/18; D01F 8/18 20060101
D01F008/18 |
Claims
2. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein said first tow and/or said second
tow comprise a spreading/commingling enhancement agent.
3. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein said first tow and said second tow
have the same tensile modulus and the same filament count.
4. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein the tensile modulus of said first
tow is the same as the tensile modulus of the second tow and
wherein the filament count of said first tow is different from the
filament count of said second tow.
5. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein the tensile modulus of said first
tow is different from the tensile modulus of the second tow and
wherein the filament count of said first tow is the same as the
filament count of said second tow.
6. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein the tensile modulus of said first
tow is different from the tensile modulus of the second tow and
wherein the filament count of said first tow is different from the
filament count of said second tow.
7. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein the second carbon filaments have a
linear weight that is greater than the linear weight of said first
carbon filaments.
8. The method for increasing the filament count of a carbon fiber
tow to form a combined tow according to claim 1 wherein said second
spread tow has a width of from 4 to 6 centimeters.
9. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein said first spread tow is under a
lengthwise tension of from 50 to 150 grams and said second spread
tow is under a lengthwise tension of from 50 to 150 grams.
10. The method for increasing the filament count of a carbon fiber
tow according to claim 1 wherein the velocity of said first gas
stream is substantially the same as the velocity of said second gas
stream.
13. The method for increasing the filament count of a carbon fiber
tow to form a combined tow according to claim 1 which includes the
additional step of applying a sizing agent to said entangled tow or
said combined tow to form a sized combined tow.
14. The method for increasing the filament count of a carbon fiber
tow according to claim 2 which includes the additional step of
applying a sizing agent to said entangled tow or said combined tow
to form a sized combined tow.
15. The method for increasing the filament count of a carbon fiber
tow according to claim 1 which includes the additional step of
combining said combined tow with an uncured resin matrix.
16. The method for increasing the filament count of a carbon fiber
tow according to claim 15 which includes the additional step of
curing said uncured resin matrix.
17. A combined carbon fiber tow that has been made by the method of
claim 1.
18. A combined carbon fiber tow that has been made by the method of
claim 2.
19. A combined carbon fiber tow that has been made by the method of
claim 14.
20. A prepreg that has been made according to the method of claim
15.
21. A composite part that has been made according to the method of
claim 16.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates generally to carbon fiber tows
that are composed of carbon filaments. More particularly, the
present invention is directed to methods for increasing the
filament count of any given carbon fiber tow by physically
incorporating one or more other carbon fiber tows directly into the
tow.
2. Description of Related Art
[0002] Composite materials include a fibrous reinforcement
structure and a resin matrix as the two principal components.
Composite materials typically have a rather high strength to weight
ratio. As a result, composite materials are used in the aerospace
industry where the high strength and relatively light weight of
composite structures are of particular importance.
[0003] Carbon fibers are a popular fibrous reinforcement for
composite materials. Carbon fibers are typically provided as a
multifilamentary yarn that is commonly referred to as a "tow".
Carbon fiber tows typically contain from 1,000 to 50,000 individual
filaments. Commercially available carbon fiber tows contain, for
example, approximately 3000 filaments (3K), 6000 filaments (6K),
12000 (12K) filaments or 24000 (24K) filaments. The linear weight
of a single carbon filament is typically in the range of from 0.02
to 0.5 milligrams per meter.
[0004] The linear weight of a carbon fiber tow depends upon the
number of filaments, their linear weight and the weight of any
coatings or other tow treatments. HexTow.RTM. AS4 is a type of
carbon fiber tow that is available form Hexcel Corporation (Dublin,
Calif.). The 3K version of HexTow.RTM. AS4 carbon fiber tow has a
linear weight of approximately 0.21 grams per meter with the 6K and
12 K versions having linear weights, respectively, of approximately
0.43 grams per meter and approximately 0.86 grams per meter.
HexTow.RTM. IM7 is another type of carbon fiber tow that is also
available from Hexcel Corporation (Dublin, Calif.). HexTow.RTM. IM7
carbon fiber tows have a higher tensile strength and tensile
modulus than HexTow.RTM. AS4 carbon fiber tows. The linear weight
of a 6K HexTow.RTM. IM7 carbon fiber tow is approximately 0.22
grams per meter with the 12K version having a linear weight of
approximately 0.45 grams per meter.
[0005] The filaments in carbon fiber tows are not twisted in the
same manner as conventional yarns. Instead, the filaments in a
carbon fiber tow are substantially parallel to each other. As a
result, carbon fiber tows tend to have a flat tape-like
cross-sectional shape. The carbon filaments are entangled with each
other to provide some cohesiveness to the tow so that is can be
handled and processed to some degree without falling apart. The
cohesiveness of a carbon fiber tow is commonly measured by
determining the "spreadability" of the tow. Tow evaluation testing
machines are available commercially for use in determining a number
of carbon fiber tow properties, including spreadability. For
example, a tow evaluation testing machine is available from
Textechno H. Stein GmbH & Co. KG (Moenchengladbach, Germany)
under the tradename ROVINGTEST. Tow evaluation test Brach ices or
equipment are common in the textile industry.
[0006] Spreadability is determined in a typical tow evaluation test
machine by placing the tow under a pre-determined tension and
passing it over a series of spreader bars. The width of the tow is
measured before the spreader bars (W1) and immediately after the
spreader bars (W2). The spreadability of the tow is equal to W2/W1.
Spreadability values (W2/W1) on the order of 1.2 to 2.2 are typical
for carbon fiber tows depending upon the filament count, filament
linear weight, type of filament, degree of filament entanglement
and post-formation treatments, such as the application of a sizing
or other coating.
[0007] Carbon filaments are relatively fragile. Accordingly, carbon
filaments are susceptible to damage during the production of carbon
fiber tows and subsequent handling. Tow fuzz or fuzziness refers to
broken filaments and fluff that may be present on the surface of a
carbon fiber tow. Test equipment for measuring the amount of fuzz
present on the surface of a carbon fiber tow are commercially
available. The amount of fuzz is expressed as a fuzz count or fuzz
value. An exemplary testing device for measuring the fuzz count of
a carbon fiber tow is the FRAY VIEW yarn defects visualization
device that is available from Lenzing Instruments GmbH & Co. KG
(Gampem, Austria). The FRAY VIEW device measures fuzz count using
an optical sensor and high resolution digital camera.
[0008] The fuzz count of a carbon fiber tow will vary depending
many factors including how the tow was processed and handled,
filament count, filament linear weight, type of filament and
post-formation treatments, such as the application of a sizing or
other coating. In general, it is desirable that the carbon fiber
tow have a fuzz count that is as low as possible. However, there
are situations, where some degree of filament breakage is desired,
For example, breaking filaments in carbon fiber tows has been used
to increase Z-direction electrical conductance in carbon fiber
composite laminates. In these situations, fuzz count is measured
and monitored to ensure that the carbon fiber tow has the desired
level of filament breakage.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, the filament count
of a first carbon fiber tow is increased by physically combining a
second carbon fiber tow with the first carbon fiber tow to form a
combined tow. It was discovered that the two carbon fiber tows
could be physically combined to provide a cohesive combined tow
that exhibits a spreadability which is close to the spreadability
of the first and second tows. It was further discovered that such a
combined tow could be formed without unduly increasing the amount
of damaged filaments present in the first or second tow.
[0010] The present invention is based on a method for increasing
the filament count of a carbon fiber to form a combined tow where a
first tow composed of first carbon filaments and having a first tow
width is passed into a spreading/commingling zone where it is
subjected to a first gas stream to four a spread first tow. A
second tow composed of second carbon filaments and having a second
tow width is also passed into the spreading/commingling zone where
it is subjected to the first gas stream to form a spread second
tow.
[0011] As a feature of the invention, the spread first tow and
spread second tow are contacted together to form contacted spread
tows which are passed over a grating so that the first and second
tows are in contact with each other and the grating. A second gas
stream, which may be a portion of the first gas stream, is passed
through the grating to provide commingling of the first and second
carbon filaments to form an entangled tow having an entangled tow
width. The entangled tow is then formed into the combined tow.
[0012] As another feature of the invention, the first and second
tows include a spreading/commingling enhancement agent that is
applied to the tows prior to spreading in the spreading/commingling
zone. It was discovered that use of a spreading/commingling
enhancement agent allows levels of filament spreading, commingling
and entanglement to be obtained that are required to form a
suitable combined tow without generating excessive broken filaments
or fuzz.
[0013] The present invention may be used to form combined tows
where the first and second tows have an equal number of the same
type of carbon filaments. As an additional feature, combined tows
with a variety of properties, such as tensile modulus, tensile
strength and linear weight, may be made by using first and second
tows that have different filament counts and/or types of carbon
filaments.
[0014] The present invention is not only directed to the method of
increasing the filament count of a carbon fiber tow, but also is
directed to the combined tows made in accordance with the invention
including unidirectional carbon fiber tape and woven carbon fiber
products. The invention is also directed to uncured composite
materials made using the combined tows, such as prepreg. The
invention is further directed to composite parts made from the
uncured composite materials.
[0015] The above described and many other features and attendant
advantages of the present invention will become better understood
by reference to the following detailed description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a partially diagrammatic side view of an exemplary
method for increasing the filament count of a carbon fiber tow in
accordance with the present invention.
[0017] FIG. 2 is a partially diagrammatic top view of the exemplary
method shown in FIG. 1.
[0018] FIG. 3 is a side view of a portion of an exemplary grating
showing the downward displacement of the carbon filaments due to
the gas stream being passed through the grating during formation of
the entangled tow.
[0019] FIGS. 4A-4E show cross-sectional representations of the
starting tows and the different tow configurations at various
stages during the method.
[0020] FIG. 5 is a detailed partial sectional view of a preferred
exemplary consolidation reel that is used in forming an entangled
tow into a combined tow.
[0021] FIG. 6 is a representational sectional view of a portion of
an exemplary hybrid combined tow which includes a first tow that
has carbon fiber filaments which are different from the carbon
fiber filaments in the second tow.
DETAILED DESCRIPTION OF THE INVENTION
[0022] A preferred exemplary system for carrying out the method of
increasing filament count of a carbon fiber tow in accordance with
the present invention is shown at 10 in FIGS. 1 and 2. A first tow
12 is fed into a spreading/commingling zone 14 (outlined in
phantom) via a feed roller 16. The spreading/commingling zone 14
may be an enclosed space, such as chamber, or it may be an open
space where spreading and commingling of the tows is carried out.
Any type of carbon fiber tow that is composed of from 2,000 to
50,000 carbon filaments may be used as the first tow 12. Preferred
carbon fiber tows are those that are commercially available and
have a filament count of 3K (approximately 3000 filaments), 6K
(approximately 6,000 filaments) or 12K (12000 carbon
filaments).
[0023] The first tow 12 may have a variety of tensile strengths and
tensile moduli. For example, the carbon fiber tow used as first tow
12 preferably has a tensile strength of from 750 to 900 ksi, a
tensile modulus of from 35 to 45 Msi, a strain at failure of 1.5 to
2.5%, a density of 1.6 to 2.0 g/cm.sup.3 and a linear weight of
from 0.3 to 1.0 g/m (2,700 denier to 9,000 denier). The first tow
12 may alternately be a lower modulus tow which has a tensile
strength of from 600 to 700 ksi, a tensile modulus of from 30 to
5.5 Msi, a strain at failure of 1.5 to 2.5%, a density of 1.6 to
2.0 g/cm.sup.3 and a linear weight of from 0.3 to 1.0 g/m (2,700
denier to 9,000 denier)
[0024] A preferred carbon fiber tow for use as the first tow 12 is
HexTow.RTM. 12K IM7 carbon fiber tow, which has a tensile strength
of 810 ksi, a tensile modulus of 40 Msi, a strain at failure of
1.9%, a density of 1.78 g/cm.sup.3 and a linear weight of 0.446 g/m
(4014 denier). HexTow.RTM. IM7 carbon fiber tows and carbon fiber
tows with similar properties are generally considered to be
intermediate modulus carbon fiber tows. Any of the intermediate
modulus carbon fiber tows having properties similar to HexTow.RTM.
IM7 carbon fiber tow are preferred for use as first tow 12.
[0025] A lower modulus carbon fiber tow that is also preferred is
HexTow.RTM. 12K AS4 carbon fiber tow and any other carbon fiber tow
having similar properties. HexTow.RTM. AS4 carbon fiber tow has a
tensile strength of 640 ksi, a tensile modulus of 33.5 Msi, a
strain at failure of 1.8%, a density of 1.79 g/cm.sup.'and a linear
weight of 0.858 g/m (7722 denier). Any of the lower modulus carbon
fiber tows having properties similar to HexTow.RTM. AS4 carbon
fiber tow are also preferred for use as first tow 12.
[0026] FIG. 4 shows simplified cross-sectional views of the tow(s)
at positions (A)-(E) within the system 10, as indicated in FIGS. 1
and 2. A simplified cross-sectional view of the first tow 12 at
position (A) is shown in FIG. 4. The first tow 12, at position (A),
which is prior to any spreading or commingling, has a width T1 that
is between 1 and 4 mm and preferably between 1.5 and 2.5 mm. Feed
roller 16 includes a groove 18 that is provided to maintain the
desired T1 and provide alignment of the first tow 12 with the
second tow 20.
[0027] The second tow 20 may be the same carbon fiber tow as the
first tow 12 or it may be a different tow having a different
filament count and filaments having different properties provided
that the carbon fiber tow used for the second tow 20 has properties
which fall within the above outlined suitable properties for the
first tow 12. The first and second fiber tows are considered to be
the same for the purposes of this description if the filament
count, tensile strength, tensile modulus and linear weight of the
first tow are within 10 percent (preferably within 5 percent) of
the filament count, tensile strength, tensile modulus and linear
weight, respectively, of the second tow. The first and second fiber
tows are considered to be different for the purposes of this
description if the filament count, tensile strength, tensile
modulus or linear weight of the first tow individually differ by
more than 10 percent (preferably more than 5 percent) from the
filament count, tensile strength, tensile modulus or linear weight,
respectively of the second tow.
[0028] Exemplary combinations of different carbon fiber tows are:
1) the tensile modulus of the first tow is the same as the tensile
modulus of the second tow and the filament count of the first tow
is different from the filament count of the second tow; 2) the
tensile modulus of the first tow is different from the tensile
modulus of the second tow and the filament count of the first tow
is the same as the filament count of the second tow; and 3) the
tensile modulus of the first tow is different from the tensile
modulus of the second tow and the filament count of the first tow
is different from the filament count of the second tow.
[0029] Preferred exemplary combinations of first and second tows
(first tow//second tow) include the following: 1) HexTow.RTM. 12K
IM7 carbon fiber tow//HexTow.RTM. 12K IM7 carbon fiber tow; 2)
HexTow.RTM. 6K IM7 carbon fiber tow//HexTow.RTM. 12K IM7 carbon
fiber tow; 3) HexTow.RTM. 12K AS4 carbon fiber tow//HexTow.RTM. 12K
AS4 carbon fiber tow; 4) HexTow.RTM. 6K AS4 carbon fiber
tow//HexTow.RTM. 12K AS4 carbon fiber tow; 5) HexTow.RTM. 12K IM7
carbon fiber tow//HexTow.RTM. 12K AS4 carbon fiber tow; 6)
HexTow.RTM. 12K AS4 carbon fiber tow//HexTow.RTM. 12K AS4 carbon
fiber tow; 7) HexTow.RTM. 6K AS4 carbon fiber tow//HexTow.RTM. 12K
IM7 carbon fiber tow; and 8) HexTow.RTM. 6K IM7 carbon fiber
tow//HexTow.RTM. 12K AS4 carbon fiber tow.
[0030] The description herein is directed to HexTow.RTM. 12K IM7
carbon fiber tow and HexTow.RTM. 12K AS4 carbon fiber tow for
exemplary purposes and to set forth the preferred embodiments of
the invention. The invention also may also be used to increase the
filament count of many other types of commercially available carbon
fiber tows, such as HexTow.RTM.AS2C, HexTow.RTM.AS4C,
HexTow.RTM.AS7, HexTow.RTM.IM8. HexTow.RTM.IM9, HexTow.RTM.IM5 and
carbon fiber tows available from other commercial sources that have
similar properties.
[0031] A simplified cross-sectional view of the second tow 20 at
position (A) is also shown in FIG. 4. The second tow 20, at
position (A), which is prior to any spreading or commingling, has a
width T2 that is between 1 and 4 mm and preferably between 1.5 and
2.5 mm. Feed roller 22 includes a groove 24 that is provided to
maintain the desired T2 and provide alignment of the second tow 20
over the first tow 12.
[0032] The first tow 12 and second tow 20 are preferably provided
to their respective alignment reels 16 and 22 from standard spools
of carbon fiber tow (not shown). If desired, the system 10 may be
incorporated into an existing carbon fiber production line where
carbon fiber tows can be fed directly to the alignment reels 16 and
22 without first being wound onto a storage spool.
[0033] The spreading/commingling zone 14 includes an inlet 26, and
outlet 28, a left side 30, a right side 32, a top 34 and a bottom
36. The first tow 12 includes a plurality of first carbon filaments
that extend in a first tow lengthwise direction as indicated by
arrow 38. The first tow 12 has a first tow filament count, which is
preferably from 3K to 24K. The second tow 20 includes a plurality
of first carbon filaments that extend in a second tow lengthwise
direction as indicated by arrow 40. The second tow 20 has a second
tow filament count, which also is preferably from 3K to 24K.
[0034] The speed at which the first and second tows are fed through
inlet 26 into the spreading/commingling zone 14 can be as low as 2
meters/minute and as high as 10 meters/minute. Tow feed speeds
slower than 2 meters/minute results in disruption of the filaments
and damage without any increase in cohesiveness of the combined
tow. Tow feed speeds above 10 meters/minute do not allow for
sufficient commingling and entanglement to provide a combined tow
having the desired low spreadability. The preferred tow feed speed
for 6K-12K carbon fiber tows is between 5-8 meters/minute.
[0035] At point (B) within the spreading/commingling zone 14, a
first gas stream, as represented by arrows 42, is passed
transversely through the first tow 12 and second tow 20 to provide
lateral spreading of the tows. The first gas stream is preferably a
stream of air. Other gases may be used provided they do not
adversely affect the tows. For example, a gas stream composed
substantially of nitrogen may be used in situations where an inert
environment is desired.
[0036] The velocity of the first gas stream 42 and the lengthwise
tensions applied to the first tow 12 and second tow 22 at point (B)
are selected to provide gas-induced or pneumatic spreading of the
tows. The downward velocity of the first gas stream 42 should be
from 10 to 25 meters/second and preferably from 15 to 20
meters/second. The lengthwise tension on the first tow 12 should be
from 50 to 150 grams. The lengthwise tension on the second tow 20
should also be from 50 to 150 grams. For 6K and 12K carbon fiber
tows, the preferred tension at point (B) is from 90 to 110
grams.
[0037] At point (B), the second tow 20 remains aligned directly
above the first tow 12 as both tows are pneumatically spread to
form a spread first tow 44 and spread second tow 46. The spread
first tow 44 has a spread first tow width (ST1) and the spread
second tow has a spread second tow width (ST2). The tows do not
contact each other during the spreading operation. It was found
that contact between the tows prior to completion of the spreading
step had a negative effect on the subsequent commingling of the
tows.
[0038] The tow feed speed, first gas stream velocity and tow
tensions are chosen to provide a degree of spreading for the first
tow and second tow that is necessary to form a cohesive combined
tow. The first tow 12 should be spread so that the ratio between
ST1 and T1 is from 5:1 to 25:1. An ST1 to T1 ratio of from 8:1 to
12:1 is preferred for 6K and 12K carbon fiber tows. The second tow
20 should be spread so that the ratio between ST2 and T2 is from
15:1 to 40:1. An ST2 to T2 ratio of from 20:1 to 30:1 is
preferred.
[0039] When the first and second tows are the same carbon fiber
tow, the second tow 20 tends to be spread more than the first tow
12 due to the second tow being located directly above the first tow
12 in the first gas stream 42. It was found that initially wider
tows tend to spread more in the first gas stream than narrower
tows. It was also found that tows, having larger diameter filaments
tend to spread more in the first gas stream.
[0040] The orientation of the tows in the first gas stream, as well
as the width of the tows and filament size, are chosen so that the
ratio between ST2/T2 and ST1/T1 is from 1.5:1 to 5:1. It is
preferred that the ratio between ST2/T2 and ST1/T1 be from 2:1 to
3:1. When the first tow and second tow are both either 6K or 12K
carbon fiber tows, the preferred ratio between ST2/T2 and ST1/T1 is
2.5:1. The tension placed on the tows affects the gas-induced
spreading. It is preferred that the tension applied to the first
tow 12 is equal to the tension applied to the second tow 20
(.+-.10%). However, the tension applied to the first and second
tows may be varied together or independently to achieve desired
levels of ST1/T1 and ST2/T2 that are require to provide desired
ratios of ST1/T1 to ST2/T2.
[0041] The spread first tow 44 and spread second tow 46 are
contacted with each other and a grating 50 at point (C) to form
contacted spread tows 48. The contacted spread tows 48 have a width
(CST). As the contacted spread tows 48 move across the grating 50
they are exposed to a second gas stream represented by arrows 52
which passes through the grating 50. The second gas stream 52
preferably has the same source as the first gas stream 42, so that
the second gas stream is a portion or part of the first gas stream.
Accordingly, the above described parameters for the first gas
stream 42 are also applicable to the second gas stream 52. It is
preferred that the first and second gas streams are the same to
provide a single gas stream that spreads and commingles the first
and second tow at the same gas stream velocity. However, there may
be situations where it is desired to use a first gas stream to
spread the first and second tows and then use a different second
gas stream to commingle the tows.
[0042] At point (C), the spread first and second tows are in
contact with each other and the grating 50. The second gas stream
52, in combination with movement of the tows over the grating 50,
causes formation of an entangled tow 56 which has a width (ET). The
width of the entangled tow 56 as it crosses grating 50 is
preferably kept relatively close to the width of the contacted
spread tows 48 so that the ratio between CST and ET remains at from
0.9:1 to 1.1:1. The tension applied to the entangled tow 56 on
grating 50 and the velocity of the second gas stream 52 are
selected to keep CST/ET in the desired range.
[0043] A partial sectional view of a preferred exemplary grating 50
is shown in FIG. 3. The grating 50 includes bars in the shape of
rods 54 which are spaced apart a distance (GS). The number of bars
in the grating, cross-sectional shape, dimensions and spacing may
be varied to achieve desired levels of commingling. The downward
force applied to entangled tow 56 by the gas stream causes a
downward displacement "D" of the entangled tows between the bars.
The tension on the entangled tow 56, the velocity of the second gas
stream 52 and GS are selected to achieve a "D" that provides
sufficient commingling without causing excessive breakage of
filaments. If the tension is too low, the tows are drawn too far
into the grating and damaged. If the tension is too high, desired
levels of spreading and commingling do not occur.
[0044] The grating 50 should have from 10 to 20 grating rods 54
that extend parallel to each other between the left edge 30 and
right edge 32 of the spreading/comingling zone 14. The rods 54
should have a diameter of 2 to 5 mm and GS should range from 3 mm
to 9 mm. D should be from 0.5 mm to 5 mm in order to achieve
sufficient commingling of the filaments without increasing fizz
count. A preferred grating for commingling 6K and 12K carbon fiber
first tows and second tows will have from 12 to 16 rods which each
having a diameter of 2 to 3 mm and a GS of 4 to 6 mm. When this
preferred grating is used to commingle 6K and/or 12K carbon fiber
tows, tow tension and the velocity of the second gas stream 52 are
selected so that D is from 1 mm to 3 mm.
[0045] The grating bars 54 are shown as rods having a circular
cross-section. Other types of grating bars are possible, such as
those having non-cylindrical arcuate cross-sectional shapes or
square/rectangular cross-sections. When grating bars with
non-cylindrical cross-sectional shapes are used, care must be taken
to control the other process parameters to ensure that adequate
commingling is obtained without causing excessive filament
breakage.
[0046] The entangled tow 56 is removed from the
commingling/spreading zone 14 through outlet 28. The entangled tow
56 is formed into a combined tow 58 by passing the entangled tow 56
over a consolidation reel 60 that has a grooved perimeter 62 which
is designed to reduce the width of the entangled tow 56 to the
width (CT) of the combined tow 58. The grooved perimeter 62 has a
concave shape which is designed to provide the desired reduction
from ET to CT without adversely affecting the commingled
filaments.
[0047] A detailed partial sectional view of the exemplary
consolidation reel 60 is shown in FIG. 5. The consolidation reel 60
is designed for use in forming 6K to 24K entangled tows 56 into
combined tows 58. The consolidation reel 60 has a radius (RR) of
from 30 to 60 mm with the groove 62 having a width (RGW) of from 10
to 25 mm and a depth (GD) of from 4 to 10 mm.
[0048] The tension applied to the entangled tow 56 as it is passed
to the consolidation reel 60 is maintained at a level which, in
combination with the groove 62, provides the desired reduction in
tow width. The width of the combined tow (CT) should be from 2 to 5
mm for combined tows containing from 6K to 24K carbon filaments.
Tension on the entangled tow 56 between point (D) and the
consolidation reel 60 should be between 300 to 500 grams.
[0049] It was discovered that an organic oil-based surfactant,
which is applied to the first and/or second tows prior to point
(B), acted as a spreading/commingling enhancement (SCE) agent to
provide desired levels of spreading and commingling of the tows
without damaging them. When subjected to the same degree of
spreading and commingling, the fuzz count of the combined tow
tended to be substantially higher when the SCE was not used.
[0050] The SCE agent can be any of the organic-oil based
surfactants that are commonly used as softening agents in the
textile industry. Exemplar SCE agents include alkoxylated castor
oil triglycerides, such as ethoxylated castor oil triglycerides.
Preferred exemplary SCE agents are polyoxyethylene castor oil
solutions which are available from Henkel Corporation (Dusseldorf,
Germany) under the trade name TRYLOX. For example, spreading and
commingling of a 12K IM7 first tow and 12K IM7 second tow was
qualitatively improved when the tows were initially treated by
being passed through a solution of TRYLOX 5918 (1% solution)
followed by drying at 135.degree. C.
[0051] The SCE agent can be applied to the first tow and/or second
tow any time prior to point (C). For example, the tows may be
passed through a bath of SCE agent and dried in-line between points
(A) and (B). Alternately, the SCE agent may be applied to the tows
at any time prior to their being passed over alignment reels 16 and
22.
[0052] Any of the sizing agents that are conventionally applied to
carbon fiber tows may also be applied to the combined tow 58. Such
conventional sizing agents include vinyl ester sizing agents,
epoxy-based sizing agents, phenolic sizing agents, polyurethane
sizing agents and the like. When a sizing agent is desired, it
should be applied only after spreading and commingling of the first
and second tows. Application of the above types of conventional
sizing agents to the tows at any point in the system prior to point
(D) was found to adversely affect the spreading and commingling of
the tows. It is preferred that the sizing, if any, is applied at a
point after the entangled tow 56 exits the spreading/commingling
zone 14.
[0053] The combined tow 58, with or without sizing, is wound onto a
take up spool 64 for storage and further use. The combined tow 58
may be used in the same manner as any other carbon fiber tow to
make a wide variety of composite materials. For example, combined
tow 58 may be formed into unidirectional tape or woven fabric, and
combined with an uncured thermoplastic or thermosetting resin
matrix to form a wide variety of prepreg and molding compounds that
may be cured/molded to form composite parts.
[0054] A preferred example of practice in which the filament count
of a carbon fiber tow is increased using the same type of carbon
filaments is as follows: a combined tow 58 was made using system 10
in which the first tow 12 was HexTow.RTM. 12K IM7 carbon fiber tow
and the second tow 20 was HexTow.RTM. 12K IM7 carbon fiber tow. T1
and T2 were both 2 mm and the line speed through inlet 26 was 3
meters/minute with the tension on the first and second tows being
100 grams each. Both the first tow and second tow were passed at
the line speed through a 1% solution of TRYLOX 5918 and dried at
135.degree. C. prior to being spread and commingled in the
spreading/commingling zone 14. The velocity of the first and second
air streams 42 and 52 was the same at 20 meters/second. The ratio
of ST1 to T1 was 10:1 and the ratio of ST2 to T2 was 25:1. The
grating 50 contained 14 grating bars 54. The diameter of each
grating bar 54 was 2.3 mm and GS was 4.7 mm. Tension on the
entangled tow 56 was 400 grams and the width (CT) of the combined
tow 58 was 3 mm. It should be noted that the preceding method
parameters are approximate values and ma each be varied .+-.15%
without adversely affecting the formation of a combined tow 58
which has the desired spreadability and fuzz count.
[0055] The spreadability of the combined tow 58 (24K filaments),
made as described above, was measured using tow evaluation
equipment similar to the ROVINGTEST tow evaluation equipment. The
spreadability of the combined tow 58 was 1.7 (.+-.10%). The
spreadability of standard HexTow.RTM. 24K IM7 carbon fiber tow was
also measured on the same tow evaluation equipment. The
spreadability of the standard HexTow.RTM. 12K IM7 carbon fiber tow
was 2.0 (.+-.10%).
[0056] The above example demonstrates that combined tows made in
accordance with the present invention are sufficiently cohesive
that they have a spreadability which is equal to or less than the
spreadability of the standard commercially available tow having the
same filament count. It is preferred that the spreadability of the
combined tow is equal to or less than the spreadability of a
standard commercial tow having the same filament count when
measured using the same testing equipment. However, the method and
system of the present invention is also useful in making combined
tows generally where the spreadability of the combined tow, when
measured on the same test equipment, is within 25% of the
spreadability of a similar commercially available tow having the
same filament count.
[0057] Fuzz counts of the combined tow (24K filaments) and standard
HexTow.RTM. 12K IM7 carbon fiber tow were determined using test
equipment similar to the FRAY VIEW yarn defects visualization
device. The fuzz counts of the combined tows were less than 25%
above the fuzz counts for the standard HexTow.RTM. 12K IM7 carbon
fiber tow.
[0058] A preferred example of practice for making a. hybrid
combined tow where the filament count of a carbon fiber tow is
increased using different carbon filaments is as follows: a
combined tow 58 was made using system 10 in which the first tow 12
was HexTow.RTM. 12K IM7 carbon fiber tow and the second tow 20 was
HexTow.RTM. 12K AS4 carbon fiber tow. T1 was 2 mm and T2 was 2.5-3
mm. The system and method parameters were otherwise the same as set
forth in the above preferred example. The ratio of ST1 to T1 was
10:1 and the ratio of ST2 to T2 is 30:1. CT was 4 mm. These are
also approximate values which, like the parameters mentioned above,
may be varied by .+-.15%.
[0059] Spreadability and fuzz counts can be measured for the hybrid
combined tow and commercially available HexTow.RTM. 12K AS4 carbon
fiber tow in the same manner as described above for the 12K
IM7//12K IM7 combined tow and commercially available HexTow.RTM.
12K IM7 carbon fiber tow. The spreadability of the hybrid combined
tow will be 2.0 (.+-.10%) and the spreadability of the HexTow.RTM.
12K AS4 carbon fiber tow will be 2.0 (.+-.10%). This example
demonstrates that 12K IM7//12K AS4 hybrid combined tows can be made
in accordance with the present invention that have spreadability
(cohesiveness) that compares favorably to the spreadability of both
HexTow.RTM. 12K IM7 and HexTow.RTM. 12K AS4.
[0060] The fuzz counts of the hybrid combined tow and HexTow.RTM.
12K AS4 can also be measured as in the preceding example. The fuzz
count of the hybrid combined tow is expected to be less than 25%
above the fuzz counts for either commercially available HexTow.RTM.
12K IM7 or HexTow.RTM. 12K AS4.
[0061] The filaments of HexTow.RTM. 12K IM7 carbon fiber tow have a
diameter that is less than the filament diameter of HexTow.RTM. 12K
AS4 carbon fiber tow. A cross-section of the hybrid combined tow
was viewed microscopically to determine the homogeneity of filament
commingling based on the different filament diameters. It was found
that the hybrid combined fiber had a substantially homogenous
cross-sectional mixture of IM7 and AS4 filaments. Such a homogenous
commingling of the filaments is a particular advantage in
accordance with the present invention when carbon fiber tows having
different properties are combined. A representational sectional
view of the hybrid combined tow is shown in FIG. 6 where the IM7
filaments (5.2 micron diameter) are shown as 12 and the AS4
filaments (7.1 micron diameter) are shown as 20.
[0062] It should be noted that the invention is not limited to
combining a first tow with a second tow, but can also be used to
increase filament count by aligning, spreading and commingling 3 or
more tows. When combining more than two tows, the various
conditions and parameters set forth above with respect to combining
a first tow with a second tow may be varied in order to achieve
desired levels of commingling of the multiple tows and
spreadability of the combined tow.
[0063] Having thus described exemplary embodiments of the present
invention, it should be noted by those skilled in the art that the
within disclosures are exemplary only and that various other
alternatives, adaptations and modifications may be made within the
scope of the present invention. Accordingly, the present invention
is not limited by the above-described embodiments, but is only
limited by the following claims. What is claimed is: [0064] A
method for increasing the filament count of a carbon fiber tow by
forming a combined tow, said method comprising the steps of: [0065]
providing a first tow which comprises a plurality of first carbon
filaments that extend in a first tow lengthwise direction, said
first tow having a first tow filament count and a first tow width;
[0066] providing a second tow which comprises a plurality of second
carbon filaments that extend in a second tow lengthwise direction,
said second tow having a second tow filament count and a second tow
width; [0067] passing said first tow into a tow
spreading/commingling zone in said first tow lengthwise direction,
said tow spreading/comingling zone having an inlet, an outlet, a
left side, a right side, a top and a bottom, wherein said first tow
is passed through said inlet at a feed speed; [0068] passing said
second tow into said tow spreading/commingling zone in said second
tow lengthwise direction wherein said second tow is passed through
said inlet at said feed speed, said second tow being aligned above
said first tow wherein said second tow does not contact said first
tow: [0069] providing a grating located at the bottom of the
spreading/commingling zone, said grating comprising a plurality of
bars that extend parallel to each other between the left side and
right side of said spreading/commingling zone; [0070] providing a
first gas stream flowing in a direction from the top of said
spreading/commingling zone to said bottom; [0071] contacting said
first tow with said first gas stream in order to spread said first
carbon filaments apart a sufficient distance to provide a spread
first tow that has a spread first tow width, wherein the ratio of
said spread first tow width to said first tow width is from 5:1 to
25:1; [0072] contacting said second tow with said first gas stream
in order to spread said second carbon filaments apart a sufficient
distance to provide a spread second tow that has a spread second
tow width, wherein the ratio of said spread second tow width to
said second tow width is from 15:1 to 40:1 and wherein the spread
second tow width is greater than the first spread tow width; [0073]
contacting said spread first tow with said spread second tow to
form contacted spread tows; [0074] providing a second gas stream
flowing in a direction from the top of said spreading/commingling
zone to said bottom wherein said second gas stream flows through
said grating; [0075] passing said contacted spread tows over said
grating in the presence of said second gas stream to provide
commingling of said first filaments with said second filaments to
form an entangled tow which has an entangled tow width: and [0076]
forming said entangled tow into a combined tow that has a combined
tow width and combined filament count, wherein the ratio of said
entangled tow width to said combined tow width is from 5:1 to 40:1
and wherein the combined filament count is greater than said first
tow filament count or said second tow filament count.
* * * * *